Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 260226

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1026 PM EDT Sun Jun 25 2017

Dry and cool air will continue to spread in from the northwest over
the forecast area through much of the week as Canadian high pressure
remains to our north. As the high moves offshore, moist southerly
flow will return toward the end of the week through the weekend.


1020 PM update: Adjusted overnight temps/dewpts. The short-range
model that seems to be doing the best is the RAP at the moment,
and its mins are within a couple degrees of those from the previous
fcst. I weighted new hourly values more toward the RAP but kept
mins more or less as-is.

A very broad trough covers the eastern two thirds of the nation
attm.  Mid and high clouds persist over the Piedmont, associated
with a jetlet stretching from the OH river valley to the New
England. Upper level RH trends indicate some drying as the jetlet
shifts slightly east, so these clouds are expected to gradually
become more patchy with time. Patchy fog near rivers, lakes, and
bodies of water will remain possible but should be fairly shallow.

A weakly reinforcing cold front, with little to no moisture, will
move through the region on Monday to bring in slightly cooler
and drier air. Maxes will be about a category below climo Monday


As of 230 PM EDT Sunday:  The short term fcst period kicks off
on Monday evening amidst broad H5 troffing across much of the
east/central CONUS, while a series of shortwave impulses pass
through the mean flow aloft.  At the surface,  a weak/dry cold front
will be making its way into/through the high terrain of western NC
as high pressure slides east across the TN Valley.  Given the drier
nature of this fropa as well as a lack of any sig shortwave energy,
will keep the fcst dry through the overnight hours.  However,
by early/mid Tuesday afternoon a slightly more potent shortwave
will accompany another reinforcing cold front, which will dive
through the OH valley into east TN/KY then western VA/WVA by
Tuesday evening.  Given improved convergence along the front as
well as weak upper forcing thanks to the shortwave, think convection
will be possible across the aforementioned areas, eventually moving
at/into western NC by late day Tuesday.  Therefore the fcst will
feature slight/chance pops across portions of western NC with the
highest pops being across the mtns along/north of I40.  Beyond that,
broad surface high pressure will consume the fcst area for Wednesday
leading to pleasant conditions.  Temperatures/dewpoints will be the
primary highlight of this fcst period as highs top out each day
nearly 6-8 degrees below normal, with dewpoints in the lower/mid
50s yielding low RH values.


As of 155 PM EDT Sunday: No sigfnt changes needed to the going fcst.
The models continue to show the transition from a unseasonal trof /
Canadian sfc high config into more of a normal summertime pattern.
There shud be enuf llvl moisture adv for mtn top convg shrs/tstms
Thu afternoon but coverage will be limited as upper heights rise and
a subtrop ridge noses in from the east. Things become more
interesting Fri thru the period as sfc-based instability increases
and easily breaks a weak cap each afternoon allowing for stronger
diurnal convection with better coverage...mainly across the higher
terrain Fri. Mid level LRs increase to arnd 6.5 C/km on Sat associated
with an incoming h5 s/w which will develop stg/svr activity over the
mtns/fthills spreading east across the piedmont regions thru the
late afternoon and evening. A cold front approaches the FA late Sat
and there is decent agreement in the guidance to suspect the front
will push into the FA and become quasi-stationary Sun. Thus...above
normal coverage will be had with thunder activity developing within
a continued unstable atmos. Max temp will begin the period a little
lower than normal and increase to near or just above normal by the
weekend. Mins will also rebound to normal levels in an increasingly
moist environ.


At KCLT and elsewhere: A persistent area of enhanced upper level
flow over the Ohio Valley and Northeast states, in the exit
region of a trough, will continue to bring some high cloud cover
overnight. However, the axis of better moisture should gradually
shift east and lead to partial clearing. Flow will remain light
northerly through most if not all of the period. Some guidance
suggests lee troughing after 18z Mon and associated backing, but
confidence is low on wind shifting out of the NW quad, except at
KAND. Low level conditions appear much too dry for restrictions
except in the Little TN River valley of SW NC.

Outlook: Light winds and VFR conditions should continue through
most of the week. Return flow moisture will return around the
offshore ridge Thursday into Friday.

Confidence Table...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     High 100%

The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:




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